Helical Trochoidal Rotary Machines

ABSTRACT

Rotary positive displacement machines with trochoidal geometry that comprise a helical rotor that undergoes planetary motion within a helical stator are described. The rotor can have a hypotrochoidal cross-section, with the corresponding stator cavity profile being the outer envelope of the rotor as it undergoes planetary motion, or the stator cavity can have an epitrochoidal cross-section with the corresponding rotor profile being the inner envelope of the trochoid as it undergoes planetary motion. In some multi-stage embodiments, the rotor-stator geometry remains substantially constant along the axis of the rotary machine. In other multi-stage embodiments, the rotor-stator geometry varies along the axis of the rotary machine.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority benefits fromInternational Application No. PCT/CA2019/051272 filed on Sep. 10, 2019,entitled “Helical Trochoidal Rotary Machines”. The '272 application isrelated to and claims priority benefits from U.S. Provisional PatentApplication Ser. No. 62/729,763 filed Sep. 11, 2018 entitled “HelicalTrochoidal Rotary Machines”, U.S. Provisional Patent Application Ser.No. 62/730,025 filed Sep. 12, 2018 entitled “Helical Trochoidal RotaryMachines With Offset”, and U.S. Provisional Patent Application Ser. No.62/783,088 filed Dec. 20, 2018 entitled “Sealing In Helical TrochoidalRotary Machines”. The '272, '763, '025 and '088 applications are eachhereby incorporated by reference herein in their entireties.

FIELD OF THE INVENTION

The present invention relates to rotary positive displacement machines,particularly rotary machines with trochoidal geometry that comprise ahelical rotor that undergoes planetary motion within a helical stator.

BACKGROUND OF THE INVENTION

Rotary machines, in which at least one rotor has planetary motion withina stator or housing, can be employed, for example, as positivedisplacement pumps, rotary compressors, vacuum pumps, expansion engines,and the like.

Pumps are devices that can move a working fluid from one place toanother. There is a wide range of end uses for various types of pumps,including irrigation, fire-fighting, flood control, water supply,gasoline supply, refrigeration, chemical movement and sewage transfer.Rotary pumps are typically positive displacement pumps comprising afixed housing, gears, cams, rotors, vanes and similar elements. Rotarypumps usually have close running clearances (only a small distance orgap between their moving and stationary parts), do not require suctionor discharge valves, and are often lubricated only by the fluid beingpumped.

A positive displacement pump moves fluid by trapping a volume of fluidin a chamber and forcing the trapped volume into a discharge pipe. Somepositive displacement pumps employ an expanding chamber on the suctionside and a decreasing chamber on the discharge side. Fluid flows intothe pump intake as the chamber on the suction side expands, and thefluid flows out of the discharge pipe as the chamber collapses. Theoutput volume is the same for each cycle of operation. An ideal positivedisplacement pump can produce the same flow rate at a given pump speedregardless of the discharge pressure.

Various classes of rotary machines based on trochoidal geometries areknown. Such rotary machines comprise a rotor or stator whosecross-section is bounded by a certain family of curves, known astrochoids or trochoidal shapes. These include machines with thefollowing configurations:

(1) rotary machines in which the rotor is hypotrochoidal incross-section, and undergoes planetary motion (spins about its axis andorbits eccentrically) within a stator that is shaped as an outerenvelope of that rotor (with the rotor having one more apex or lobe thanthe stator cavity);

(2) rotary machines in which the stator cavity is hypotrochoidal incross-section, and the rotor undergoes planetary motion within thestator and is shaped as the inner envelope of that stator (with therotor having one less apex or lobe than the stator cavity);

(3) rotary machines in which the rotor is epitrochoidal incross-section, and undergoes planetary motion within a stator that isshaped as an outer envelope of that rotor (with the rotor having oneless apex or lobe than the stator cavity); and

(4) rotary machines in which the stator cavity is epitrochoidal incross-section, and the rotor undergoes planetary motion within thestator and is shaped as the inner envelope of that stator (with therotor having one more apex or lobe than the stator cavity).

Thus, in all of these configurations, the rotor or stator is atrochoidal component, meaning it has a cross-sectional shape that is atrochoid.

Generally, as used herein, an object is said to undergo “planetarymotion” when it spins about one axis and orbits about another axis.

Rotary machines, such as those described above, can be designed forvarious applications including, for example, pumps, compressors, andexpansion engines. The design, configuration and operation of differentrotary machines can offer particular advantages for certainapplications.

Progressive cavity pumps (PCPs) are another type of rotary positivedisplacement machine that can offer advantages for certain applications.In PCPs, a rotor is disposed and rotates eccentrically within a helicalstator cavity. The material to be pumped (typically a fluid) follows ahelical path along the pump axis. The rotor is typically formed of rigidmaterial and the stator (or stator lining) of resilient or elastomericmaterial. The rotor is typically helical with a circular transversecross-section displaced from the axis of the helix, and defines asingle-start thread. The corresponding stator cavity is a double helix(two-start thread) with the same thread direction as the rotor, and intransverse cross-section has an outline defined by a pair of spacedapart semi-circular ends joined by a pair of parallel sides. The pitch(the axial distance between adjacent threads) of the stator is the sameas the pitch of the rotor, and the lead of the stator (the axialdistance or advance for one complete turn) is twice that of the rotor.

In PCPs, the rotor generally seals tightly against the elastomericstator as it rotates within it, forming a series of discretefixed-shape, constant-volume chambers between the rotor and stator. Thefluid is moved along the length of the pump within the chambers as therotor turns relative to the stator. The volumetric flow rate isproportional to the rotation rate. The discrete chambers taper downtoward their ends and overlap with their neighbors, so that the flowarea is substantially constant and in general, there is little or noflow pulsation caused by the arrival of chambers at the outlet. Theshear rates are also typically low in PCPs in comparison to those inother types of pumps. In PCPs, where the rotor touches the stator, thecontacting surfaces are generally traveling transversely relative to oneanother, so small areas of sliding contact occur.

SUMMARY OF THE INVENTION

In one aspect, a rotary machine comprises a stator and a rotor disposedwithin the stator; the rotor has a helical profile, and a rotor axis,and has a hypotrochoidal shape at any cross-section transverse to saidrotor axis, along at least a portion of a length of the rotor; and thestator has a helical profile, a stator axis, and has a shape at anycross-section transverse to the stator axis along at least a portion ofa length of the stator that is an outer envelope formed when thehypotrochoidal shape of the rotor undergoes planetary motion. The rotoris configured to undergo planetary motion within the stator.

In some embodiments, the hypotrochoidal shape has n lobes, where n is aninteger, the outer envelope shape has (n−1) lobes, the pitch of therotor is the same as the pitch of the stator; and the ratio of the leadof the rotor to the lead of the stator is n:(n−1). In some suchembodiments, the hypotrochoidal shape is an ellipse, n=2, the pitch ofthe rotor is the same as the pitch of the stator, and the ratio of thelead of the rotor to the lead of the stator is 2:1.

In another aspect, a rotary machine comprises a stator and a rotordisposed within the stator; the stator has a helical profile, a statoraxis, and has an epitrochoidal shape at any cross-section transverse tothe stator axis, along at least a portion of a length of the stator; therotor has a helical profile, a rotor axis, and has a shape at anycross-section transverse to the rotor axis, along at least a portion ofa length of the rotor, that is an inner envelope formed when theepitrochoidal shape of the stator undergoes planetary motion. The rotoris configured to undergo planetary motion within the stator.

In some embodiments, the epitrochoidal shape of the stator has n−1lobes, where n is an integer; the inner envelope shape of the rotor hasn lobes; the pitch of the rotor is the same as the pitch of the stator;and the ratio of the lead of the rotor to the lead of the stator isn:(n−1). In some such embodiments, n=2, and the ratio of the lead of therotor to the lead of the stator is 2:1.

In some embodiments of the rotary machines described in both aspectsabove, the rotary machine is a multi-stage machine and a plurality ofchambers are formed between cooperating surfaces of the rotor and thestator. In some embodiments, each of the plurality of chambers hasapproximately the same volume and, in some such embodiments, each of theplurality of chambers has approximately the same dimensions and shape.In some embodiments, at least one of the plurality of chambers hasdimensions that are different from another of the plurality of chambers.In some embodiments, each of the plurality of chambers has differentdimensions. In some embodiments, at least one of the plurality ofchambers has a volume that is different from another of the plurality ofchambers. In some embodiments, each of the plurality of chambers has adifferent volume.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1G (Prior Art) are schematic diagrams illustrating, intransverse cross-section, the geometry of an elliptical rotor and statorassembly at different stages of a single revolution of the ellipticalrotor.

FIG. 2A shows a side view of a rotor-stator assembly showing an outercylindrical surface of the stator. FIG. 2B is a cross-sectional view ofthe rotor-stator assembly of FIG. 2A, taken in the direction of arrowsD-D, showing a helical rotor disposed within a helical stator cavity.FIG. 2C shows an end view and three cross-sectional views taken in thedirection of arrows E-E in FIG. 2A, showing the helical rotor with atwo-lobe, elliptical transverse cross-section.

FIG. 3A is a side view of a helical rotor with an elliptical transversecross-section. FIG. 3B is another side view of the helical rotor of FIG.3A, orthogonal to the view of FIG. 3A. FIG. 3C is a cross-sectional viewof the helical rotor of FIG. 3A taken in the direction of arrows A-A inFIG. 3B.

FIG. 4A is an end view of a stator with a helical cavity. FIG. 4B is atransverse cross-sectional view of the stator of FIG. 4A. FIG. 4C is anisometric view of the stator of FIG. 4A (with the dashed line indicatingthe stator cavity).

FIG. 5 illustrates a portion of a rotor-stator assembly, showing ahelical rotor disposed inside a translucent helical stator.

FIG. 6A shows a side view of a rotor-stator assembly showing an outercylindrical surface of the stator. FIG. 6B is a cross-sectional view ofthe rotor-stator assembly of FIG. 6A, showing a helical rotor disposedwithin a helical stator cavity. FIG. 6C shows an end view and variouscross-sectional views taken in the direction of arrows A-A, B-B and C-Cin FIG. 6A, showing the helical rotor with a three-lobe transversecross-section.

FIG. 7A is a side view of a helical rotor with a three-lobe transversecross-section. FIG. 7B is an isometric view of the helical rotor of FIG.7A.

FIG. 8A is side view of a stator with a helical cavity, showing an outercylindrical surface of the stator. FIG. 8B is a longitudinalcross-sectional view of the stator of FIG. 8A. FIG. 8C is anotherlongitudinal cross-sectional view of the stator of FIG. 8A orthogonal tothe cross-sectional view of FIG. 8B. FIG. 8D is an isometric view of thestator of FIG. 8A.

FIG. 9A is a side view of a rotary machine with a helical rotor-statorassembly having trochoidal geometry. FIG. 9B is a cross-sectional viewof the rotary machine of FIG. 9A, taken in the direction of arrows A-Ain FIG. 9A.

FIG. 10 is a schematic diagram illustrating the geometry of an ellipserotating about the head of a rotating radial arm.

FIG. 11 is a cross-sectional diagram illustrating a portion of arotor-stator assembly of a rotary machine.

FIG. 12 is a graph showing results of testing of a 2-stage helicaltrochoidal rotary pump in which the overall efficiency and volumetricefficiency of the pump are plotted against the number of cycles.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENT(S)

The present application relates to rotary machines in which a helicalrotor undergoes planetary motion within a stator. They can provideadvantages for various applications, some of which are discussed below.

The rotary machines are based on trochoidal geometries, with the rotoror stator having a trochoidal geometry (in transverse cross-section,i.e. perpendicular to its axis). The rotor can be hypotrochoidal, withthe corresponding stator cavity profile being the outer envelope of therotor as it undergoes planetary motion. Alternatively, the stator cavitycan have an epitrochoidal cross-sectional geometry with thecorresponding rotor profile being the inner envelope formed by thetrochoid as it undergoes planetary motion. In such machines, one or morespecific points on the envelope (whether it be the rotor or the stator)is in continuous contact with the corresponding component, and thecontact point traces a trochoidal profile as the components executetheir relative motion.

FIGS. 1A-1G are schematic diagrams illustrating the geometry of anexample of a known rotary machine where the rotor has a cross-sectionalshape that is hypotrochoidal, and the stator cavity is shaped as anouter envelope of the rotor as it undergoes planetary motion. In thisexample the hypotrochoidal rotor is an elliptical rotor. The rotor 110and stator 120 are shown at different points in time during a singlerevolution of the elliptical rotor within the stator. FIG. 1A showselliptical rotor 110 in a first position within stator 120. Stator innersurface 125 comprises an inverse apex 140. A portion of each of rotortips 130 and 135 is in contact with inner surface 125 of stator 120, andouter surface of rotor 110 is in contact with inverse apex 140. Rotor110 spins about its center and rotates eccentrically in the directionindicated by arrow X-X (counter-clockwise) about axis 115. FIG. 1B showselliptical rotor 110 in a second position after rotor 110 has rotated. Aportion of each of rotor tips 130 and 135 remains in contact with statorinner surface 125, and outer surface of rotor 110 remains in contactwith inverse apex 140. FIG. 1C shows elliptical rotor 110 in a thirdposition after further rotation. FIG. 1D shows elliptical rotor 110 in afourth position with its major axis oriented vertically, as indicated bydashed line V-V. A portion of rotor tip 130 is in contact with inverseapex 140 and a portion of rotor tip 135 is in contact with stator innersurface 125 directly above inverse apex 140. For the remainder of thedescription below for FIGS. 1E-1G, reference numerals have been omittedfor clarity. FIGS. 1E-1G show elliptical rotor 110 after furtherrotations in a counter-clockwise direction. FIG. 1F shows ellipticalrotor 110 in a position with its major axis oriented horizontally, asindicated by dashed line H-H. Thus, inner surface 125 of stator 120 incross-section is designed such that at least a portion of each of rotortips 130 and 135 is in contact with stator inner surface 125 at alltimes during a complete revolution of elliptical rotor 110. Inverse apex140 is in contact with the outer surface of elliptical rotor 110 at alltimes during a complete revolution of elliptical rotor 110. The contactof elliptical rotor 110 with stator 120 at three positions, as describedabove, divides the interior volume of stator 120 into three chambers(for example, as shown in FIG. 1F). When elliptical rotor 110 is incontact with stator 120 at only two distinct positions (for example whenthe major axis of elliptical rotor 110 is oriented vertically, as inFIG. 1D), elliptical rotor 110 divides the interior volume of stator 120into just two chambers. Ports (not shown in FIGS. 1A-1G) can be providedfor inflow and outflow of fluid as desired. The material being conveyed(typically a fluid) moves in an arc or circumferential direction throughthe rotary machine. Examples of such a machine are described in U.S.Patent Application Publication No. US2015/0030492, which is incorporatedby reference herein.

Herein, the terms horizontal, vertical, front, rear and like termsrelated to orientation are used in reference to the drawings with theparticular orientations as illustrated. Nonetheless, the rotary machinesand related sub-assemblies described herein can be placed in anyorientation suitable for their end-use application.

In embodiments of the present rotary machines, the hypotrochoid andouter envelope (rotor and stator transverse cross-sectional profiles,respectively) are each swept along helical paths, the axes of thosehelices being the axes of rotation of those components in that referenceframe in which both parts undergo simple rotary motion (the “centers” ofthose components). The axes of the rotor and stator helices are offsetfrom one another by a distance equal to the eccentricity of the rotor.The helical rotor and corresponding stator have the same pitch, and theratio of the lead of the rotor to the lead of the stator is the same asthe ratio of their number of lobes (which is the also the same as theratio of their number of starts). As used herein, “pitch” is defined asthe axial distance between adjacent threads (or crests or troughs, forexample, on a helix), and “lead” is defined as the axial distance oradvance for one complete turn (360°). Pitch and lead are equal withsingle start helices; for multiple start helices the lead is the pitchmultiplied by the number of starts.

Thus, in embodiments of the present rotary machines, when a transversecross-section is taken in any plane perpendicular to the axis ofrotation, the hypotrochoid and envelope (that is, the cross-sectionalshape of the rotor and stator, respectively) are seen just as they wouldbe in the usual two-dimensional profile, such as shown in FIGS. 1A-1G,for example. For example, in one embodiment, the outer surface of ahelical rotor is defined by an ellipse swept along a helical path, and acorresponding stator cavity is defined by sweeping the correspondingouter envelope along a helical path with half the lead of the helicalrotor. The rotor profile is a double-start helix, and the stator profileis a single-start helical cavity. For such a machine, when a transversecross-section is taken in any plane perpendicular to the axis ofrotation, the outer profile of the rotor and inner profile of the statorwill be similar to those illustrated for those components in FIGS.1A-1G.

FIGS. 2A-C illustrate an example of such a machine. FIG. 2A shows a sideview of a stator 220. The exterior surface of stator 220 is cylindrical.FIG. 2B is a cross-sectional view taken in the direction of arrows D-Din FIG. 2A, and shows a helical rotor 210 disposed within a helicalstator cavity 225 defined by stator 220. FIG. 2C shows an end view andvarious cross-sectional views taken in the direction of arrows E-E inFIG. 2A. Rotor 210 has an elliptical transverse cross-section, as shownin FIG. 2C. As the cross-section E-E progresses along the axis ofrotation of rotor 210, the cross-sectional profile of the rotor andstator progresses in a manner analogous to the motion over time of rotor110 within stator 120, as illustrated in FIGS. 1A-1G. In the embodimentillustrated in FIGS. 2A-2C, rotor 210 has two lobes and stator cavity225 has one lobe.

FIG. 3A is a side view of a helical rotor 300 (with an ellipticaltransverse cross-section) similar to rotor 210 of FIGS. 2A-C. FIG. 3B isanother side view of helical rotor 300, orthogonal to the view of FIG.3A. FIG. 3C shows a cross-sectional view of rotor 300 taken in thedirection of arrows A-A in FIG. 3B.

FIG. 4A is an end view, FIG. 4B is a cross-sectional view and FIG. 4C isan isometric view of a stator 400 (with the dashed line indicating thestator cavity). Stator 400 corresponds to rotor 300 of FIGS. 3A-C (inother words stator 400 can be used with rotor 300), and is similar tostator 220 of FIGS. 2A-C.

FIG. 5 illustrates an example of a portion of a machine such asillustrated in FIGS. 2A-2C, showing a helical rotor 510 disposed insidea translucent helical stator 520. The pitch of the rotor (distancebetween adjacent threads) is indicated by distance 530, and the lead ofthe rotor is indicated by distance 540. Because the rotor is adouble-start helix, the lead is twice the pitch. The pitch of the statoris indicated by distance 550 and, because the stator is a single-starthelix, distance 550 is also the lead of the stator. The rotor pitch 530and stator pitch 550 are the same. In some embodiments the rotor andstator are plastic. In other embodiments of the rotary machinesdescribed herein both the rotor and stator can be metal. In otherembodiments, depending on the application, the rotor and/or stator canbe made from ceramic, elastomeric or other suitable materials orcombinations of materials. The material(s) of the rotor can be the sameas, or different from, the material(s) of the stator.

In the embodiment illustrated in FIGS. 2A-2C, the rotor and statorsurfaces bound one complete chamber or volume per envelope revolution(each volume constituting a single stage of the machine or pump). Theboundaries of these chambers are simple helices at the “top” and“bottom” (the path of the hypotrochoid generating elements, or “points”on the envelope), and a contact curve between the rotor and stator inthe “clockwise” and “counter-clockwise” direction. These chambers do notchange size or shape as the device operates. The material to be pumped(typically a fluid) is moved in an axial direction through the pump, andthe flow velocity is substantially constant.

There is a quasi-helical contact path between the rotor and the inner“ridge” of the stator at all times during rotation of the rotor (just asthere is contact between the rotor and the inverse apex in the stator inthe machine illustrated in FIGS. 1A-1G). The contact path with thestator moves or oscillates back and forth across the helical “ridge” ofthe rotor as the rotor rotates relative to the stator (in a mannersimilar to how the contact point moves back and forth across the tips ofelliptical rotor in the machine of FIGS. 1A-1G). The rotor-statorcontact path revolves around the machine as pumping action proceeds,“threading” the fluid (or material to be pumped) in a spiral path alongthe helix, to that it is moved axially from one end of the stator cavityto the other.

Thus, the periodicity of contact between the helical rotor and statoroccurs in space (moving along a continuous contact path over time)rather than in time (with intermittent contact between surfaces such asoccurs, for example, in the machine illustrated in FIGS. 1A-1G, wherethe rotor tips only intermittently contact the inverse apex on thestator). Thus, in the present rotary machines, rather than periodicallyengaging and disengaging (or touching and separating), the contactsurfaces and any associated seals slide across one another, or in closeproximity to one another, continuously. This continuous contact linebetween rotor and stator can facilitate the provision of sealing inembodiments of the present machines.

Some embodiments of the present rotary machines operate with a smallclearance between the helical rotor and stator, but without sealsbetween them. In some embodiments it can be desirable to dispose a sealbetween these components to reduce leakage of fluid between stages.

FIGS. 6A-C illustrate another embodiment of a machine according to thepresent approach, where in cross-section, the helical trochoidal rotorhas three lobes and the stator cavity has two lobes. The rotor andstator cavity are defined by sweeping these profiles along a helicalpath. This embodiment has a rotor/stator lead ratio of 3:2. FIG. 6Ashows a side view of a cylindrical stator 620. FIG. 6B is across-sectional view taken in the direction of arrows D-D in FIG. 6A,and shows a helical rotor 610 disposed within stator cavity 625 definedby stator 620. FIG. 6C shows an end view and various cross-sectionalviews taken in the direction of arrows A-A, B-B, and C-C in FIG. 6A.Rotor 610 has rounded triangular transverse cross-section, as shown inFIG. 6C. Stator cavity has a transverse cross-sectional profile that isroughly circular with two inverse apex regions, 620A and 620B sweptalong a helical path. As one moves along the axis of rotation of rotor610, the cross-sectional profile of the rotor and stator progresses in amanner as shown in FIG. 6C.

FIG. 7A is a side view of a helical rotor 700 (with a 3-lobe, roundedtriangular transverse cross-section) similar to rotor 610 of FIGS. 6A-C.FIG. 7B is an isometric view of rotor 700.

FIG. 8A is side view of a 2-lobe stator 800. FIG. 8B is a longitudinalcross-sectional view of stator 800, and FIG. 8C is another longitudinalcross-sectional view of stator 800 (orthogonal to the cross-sectionalview of FIG. 8B). Both FIGS. 8B and 8C show the inner surface of thestator cavity. FIG. 8D is an isometric view of stator 800. Stator 800 issimilar to stator 620 of FIGS. 6A-C.

FIGS. 9A and 9B illustrate an example of a rotary machine 900 with ahelical rotor-stator assembly having trochoidal geometry. FIG. 9A is aside view of rotary machine 900, and FIG. 9B is a cross-sectional viewtaken in the direction of arrows A-A in FIG. 9A. Referring primarily toFIG. 9B, rotary machine 900 comprises helical rotor 910 and helicalstator 920 defining stator cavity 925. Rotary machine 900 furthercomprises inlet housing 930 and outlet housing 935. Drive shaft 940 isfixed to carrier 945, and is mechanically coupled via sun gear 950 andring gear 955 to cause eccentric rotation of rotor 910 within statorcavity 925. Rotary machine 900 further comprises thrust bearings 960 and965, radial bearings 970 and shaft seals 980. As rotor 910 rotates withstator cavity 925, fluid can be drawn into rotary machine 900 via inletport 990, and expelled via outlet port 995.

Most of the above description has focused on embodiments of helicaltrochoidal rotary machines with a trochoidal rotor (particularly anelliptical rotor) and corresponding outer envelope stator cavity. Inother embodiments, helical trochoidal rotary machines can have anepitrochoidal stator cavity profile and corresponding rotor (innerenvelope) profile that are each swept along helical paths. Theseembodiments have the same relative motion of the rotor and stator (withthe same orbit and spin) as machines with a trochoidal rotor andcorresponding outer envelope stator cavity.

The present approach can be applied to generate embodiments of helicalrotary machines based on a hypotrochoidal or epitrochoidal rotor (withthe corresponding stator cavity profile being the outer envelope orinner envelope, respectively of the rotor as it undergoes planetarymotion), where the components have more than two or three lobes. Suchmachines will have more chamber “edge” for each trapped volume of fluid,so may tend to have more leakage per stage, poorer solids handlingcapability, and/or higher friction if dynamic seals are used. However,for some applications, for example mud motors, such embodiments withlower speed and higher torque can offer advantages.

In variations on the helical trochoidal rotary machines describedherein, the rotor and stator profiles can be offset along their normals.For example, in some such embodiments where the rotor is hypotrochoidaland undergoes planetary motion within a stator that is shaped as anouter envelope of that rotor, the rotor and stator can havecross-sectional profiles that are inwardly offset. For example, therotor can have a cross-section, that is inwardly offset from each pointon an ellipse by a fixed distance “d” measured perpendicular to atangent to the ellipse at that point. The resulting rotor profile is nota true ellipse. The corresponding stator cavity profile can be definedas the outer envelope generated when that rotor profile undergoesplanetary motion, or defined as the correspondingly inward offset of theenvelope generated by the non-offset hypotrochoid). In other embodimentswhere the stator is epitrochoidal, and the rotor undergoes planetarymotion within the stator and is shaped as the inner envelope of thatstator, the rotor and stator can have cross-sectional profiles that areoutwardly offset. Such variations in geometry can offer additionaladvantages, while still retaining at least some of the benefits providedby helical trochoidal rotary machines.

In the rotary machines described herein, the rotor (and/or optionallythe stator) can be rotated using any suitable drive mechanism. Somenon-limiting examples of drive mechanisms are briefly discussed below.

The fundamental working principal is independent of which component ofthe machine (if any) is “fixed” and which is rotating. For example, insome embodiments the machine can be operated such that the rotor andstator each revolve around their respective centers (an inherentlybalanced design). In such embodiments, even though both components arerotating about their axes, the relative motion of the components isbasically the same as in fixed stator embodiments. In some embodiments,for example, the machine can be operated such that the stator is fixedand the rotor undergoes planetary motion within it. This is mechanicallysimple and compact, but sometimes requires counterweights to providebalance. In other embodiments, the outer stator (or housing) undergoesplanetary motion about the inner rotor. Other variations are possible.

For 2:1 (rotor:stator lobe) rotary machines with hypotrochoidal rotorwith outer envelope stator cavity, or epitrochoidal stator with innerenvelope rotor, an example of a suitable drive mechanism has an externalgear fixed to the stator meshing with an internal gear with twice asmany teeth fixed to the rotor, the distance between the gear centersbeing equal to the eccentricity of the hypotrochoid, that centerdistance being maintained by bearings fixed to each part and interactingwith an element that revolves with the rotor center; the revolvingelement being driven by a shaft passing through the sun gear. This typeof mechanism is known, and used for instance in Wankel rotary engines.Alternatively, instead of using an internal gear a pair of external gearmeshes can be used to achieve a 2:1 gear ratio with the output rotatingin the same direction as the input.

For machines with other ratios, the gear ratio can be modifiedaccordingly. In a machine having a three lobe rotor and a two lobestator, the gear ratio is 3:2. In general, for a machine having an (n+1)lobe rotor and an n lobe stator, the gear ratio can be (n+1):n. Forepitrochoid with outer envelope or hypotrochoid with inner envelopemachines, the gears can be fixed to the corresponding component, forexample, the external gear can be fixed to the rotor and the internalgear can be fixed to the stator.

Other drive mechanisms that do not involve gears can be used. Forexample, some embodiments are rotary machines in which the rotor ismounted to a flexible or angled shaft (for example, fitted withuniversal joints) so that it rotates eccentrically, and power istransmitted from the concentric rotation of one end of the drive shaftto the eccentrically rotating rotor. Thus, the shaft can be coupled toand driven by a motor, with the stator acting as a guide for the rotor.Other examples use, for example, Schmidt couplings and/or cycloidaldrive mechanisms, in lieu of gears, to provide the relative motion ofthe rotor and stator.

It is possible to make a machine based on the present approach with ahelical rotor and stator having a single stage, multiple stages or, insome embodiments, with less than a complete stage (where there is nocomplete trapped chamber or volume of fluid between the ends of thepump). For the latter, end plates can be provided at each end of therotor-stator, with an inlet port provided in one end plate and an outletport in the other. If somewhat more than one complete rotor revolutionis provided (i.e. sufficient length and number of rotor pitches that atleast one bounded volume of fluid is isolated from both ends of the pumpsimultaneously), end plates may not be needed.

In multi-stage embodiments of the present machines as described above,if the rotor-stator geometry remains substantially constant along theaxis of the machine, the volume and dimensions of the bounded volumes orfluid chambers formed between the helical rotor and the stator will bethe same, and the volume of each fluid chamber will remain constantduring operation of the machine, as the rotor rotates within the stator.This is explained further in reference to FIG. 10.

FIG. 10 is a schematic diagram illustrating the geometry of an ellipserotating about the head of a rotating radial arm. In geometricconfiguration 1000, ellipse 1010 has a center C, a major axis indicatedby dotted line A-A and a minor axis indicated by dashed line B-B. Majoraxis A-A is the longest diameter of ellipse 1010, and minor axis B-B isthe shortest diameter of ellipse 1010. Ellipse 1010 rotates about centerC at an angular velocity ω₁ in a counter-clockwise direction relative toa frame of reference in which center C is stationary. Center C islocated at the head of a rotating radial arm 1020. Radial arm 1020 haslength k and rotates about a fixed end O at an angular velocity ω₂ in acounter-clockwise direction relative to a frame of reference in whichfixed end O is stationary. If angular velocity ω₁ is negative, itindicates that rotation of ellipse 1010 about center C is in a clockwisedirection relative to a frame of reference in which center C isstationary. If angular velocity ω₂ is negative, it indicates thatrotation of radial arm 1020 about fixed end O is in a clockwisedirection relative to a frame of reference in which fixed end O isstationary.

Circle 1030 is the locus of the head of radial arm 1020 as it rotatesabout fixed end O. Line O-C is also referred to as the crank arm, andlength k is referred to as the crank radius.

Geometric configuration 1000 can represent a helical rotor assembly intransverse cross-section. In embodiments of the rotary machines asdescribed herein, it is desirable that inverse apex (or ridge) of thecorresponding helical stator is in contact with the outer surface ofhelical elliptical rotor at all times during a complete revolution ofelliptical rotor. This can be achieved by configuring the geometry 1000such that the difference between the semi-major axis of the rotor withelliptical cross-section (shown in FIG. 10 as length “a”) and thesemi-minor axis of the rotor (shown in FIG. 10 as length “b”) is twicethe crank radius, k. In other words, in preferred embodiments:

a−b=2k

If the rotor and stator pitch and all dimensions (including a, b and kas shown in FIG. 10) remain constant along the length of therotor-stator assembly, then the volume and dimensions of the fluidchambers formed between the helical rotor and the stator will be thesame along the length of the assembly. Such rotary machines can be used,for example, as pumps and, if driven at constant speed can provide afairly steady volumetric flow rate or output.

In other multi-stage embodiments, the rotor-stator geometry can bevaried, in a continuous or stepwise manner, along the axis of the rotarymachine. In some embodiments, such variations can cause the volume ofthe fluid chambers to vary along the axis of the machine, such as may bedesirable for compressor or expander applications, for example. In otherembodiments, it can be advantageous to vary the geometry of therotor-stator along the axis of the rotary machine, while keeping thevolume of the fluid chambers formed between the helical rotor and thestator approximately the same along a length of the rotor-statorassembly. Such embodiments are described in further detail below, againwith reference to FIG. 10.

Instead of the rotor and stator pitch and other parameters (including a,b and k) being constant along the axis of the machine, the rotor-statorgeometry can be varied along the axis of a rotary machine, for example,as follows:

(1) By varying the pitch of the rotor and stator. For example, the pitchcan increase in the flow direction so that the volume of the fluidchambers increases along the axis of the machine. This may be desirablefor compressor applications, for example.

(2) By varying the aspect ratio of the rotor (a/b) and keeping crankradius, k, constant, where a minus b remains equal to 2k. Thecorresponding stator profile is varied along its axis accordingly.

(3) By varying the crank radius k, where a minus b remains equal to 2k.This involves also changing the aspect ratio of the rotor by varying atleast one of dimensions a or b. The corresponding stator profile isvaried along its axis accordingly. When the crank radius is varied therotor and stator axes will be inclined relative to one another (i.e. benon-parallel).

(4) By varying the degree of offset of the rotor from a true ellipse (orhypotrochoid) along the axis of the rotor, and correspondingly varyingthe stator profile along its axis.

In some embodiments, varying one or more of these parameters can causethe volume of the fluid chambers to vary along the axis of the machine,for example, getting smaller or larger. In some embodiments, theparameters are varied so that the size of the elliptical rotorcross-section and corresponding stator is scaled or reduced linearly inthe axial direction.

In some embodiments, different rotor-stator geometries or profiles canbe used in different portions or segments of the machine to meet variousrequirements. For example, a “precompressor” section with differentdimensions but equal or slightly greater displacement can be used toreduce Net Positive Suction Head (NPSH) requirements in a pump. Adifferent geometry that is more favorable for sealing can be useddownstream along the main body of the pump. In another example, atapered embodiment can be used as a nozzle or diffuser.

In some embodiments, multiple parameters can be varied in combination sothat the volume of fluid chambers formed between the helical rotor andthe stator remains approximately the same along a length of therotor-stator assembly, with the variation of one parameter at leastpartially compensating for the variation in another parameter withrespect to the effect on the volume of the fluid chambers. For example,variations described in (2) and (3) may change the flux area, but thechange in flux area could be compensated for by, for example, increasingthe rotor-stator pitch. It can be advantageous to manipulate othercharacteristics by having a different geometry in one section of therotor-stator assembly than in another section, even if the fluidthroughput along the length is roughly or substantially constant. Forexample, it could be desirable to have a high flux area near the intake(to draw a fluid in and encapsulate it), and then gradually change thegeometry towards the discharge end.

FIG. 11 is a sketch illustrating a portion of a rotor-stator assembly1100 in cross-section, to illustrate an embodiment in which, multipleparameters are varied in combination so that the volume of the fluidchambers formed between a helical rotor 1110 and a corresponding stator1120 remains approximately the same along a length of the rotor-statorassembly. In this embodiment, the rotor and stator axes arenon-parallel. When the rotor and stator axes are non-parallel, insteadof being mapped on to plane that is perpendicular to both axes, the“cross-sectional” profile of the rotor and stator is mapped on to thesurface of a sphere which is perpendicular to both axes (the center ofsphere being the point at which the rotor axis 1115 and stator axis1125, if extrapolated, would intercept).

The crank radius, k, is the arc length (on the surface of the sphere atthat point along the axes) between the longitudinal axis 1115 of rotor1110, and the longitudinal axis 1125 of stator 1120. Crank radius, k, isvarying along the length of the assembly (decreasing toward the lowerend of the illustrated assembly), and the rotor and stator longitudinalaxes 1115 and 1125 are non-parallel. The length of minor transverse axisof the elliptical rotor 1110 mapped onto the sphere is shown in FIG. 11as 2 b. As in FIG. 10 where a−b=2k, at any point along the length ofrotor-stator assembly 1100 in FIG. 11 the major transverse axis (2 a) ofthe elliptical rotor 1110 (mapped onto the sphere) is 2b+4k. In theembodiment illustrated in FIG. 11, the crank radius k and the dimensionsof the rotor and corresponding stator are continuously scaling ordecreasing along a length of the assembly so that the rotor and statortransverse profiles at any axial position differ only in their size. Thepitch of the rotor and stator can be correspondingly increased, so thatthe volume of the fluid chambers formed between rotor 1110 and stator1120 remains approximately the same along the length of the rotor-statorassembly. In the embodiment of FIG. 1, the pitch is varied continuously,and the pitch between various pairs of points along the length of theassembly is shown gradually increasing, from P₀ to P₁ to P₂. To maintainconstant chamber volume in the case described, instantaneous pitch atany point is inversely proportional to the square of the distance tothat point from the center of the sphere (zero eccentricity point).Without such a change in pitch, the volume of fluid chamber woulddecrease, and such a machine could be used as a compressor, for example.

The changes in geometry can be continuous or gradual or there can be astep change. If the latter, preferably the eccentricity of the pumpremains constant so that single rotor and stator parts can be usedthroughout the machine, and two or more rotor sections can be driven asa single component. In embodiments with a step change, it can bedesirable to provide a space or chamber between the sections where thefluid can switch between flow paths. The pressure in this intermediatespace is preferably slightly positive, to reduce the likelihood ofcavitation. In some embodiments this can be achieved by providing aslightly smaller displacement in the upstream section. Alternatively,slip caused by pressure differential across the pump can provide thispositive pressure. It can further be desirable in some instances toprovide a pressure relief device in the intermediate space to controlload on the upstream pump section and/or “motoring” of the downstreampump section.

As with other positive displacement machines, embodiments of themachines described herein can be used as hydraulic motors, pumps(including vacuum pumps), compressors, expanders, engines and the like.The helical rotary machines described herein can provide relatively highdisplacement/pump volume for their size, relative to PCPs for example.

In one application, embodiments of the machines described herein can beused in electric submersible pump (ESP) systems, for example, asdownhole pumps in the oil and gas industry for pumping production fluidsto the surface.

In the same application, embodiments of the machines described hereincan be used for top driven submersible pumps driven by rotating shaftsconnecting a surface mounted drive system to the pump for example, asdownhole pumps in the oil and gas industry for pumping production fluidsto the surface.

Various different embodiments of the machines described herein can beparticularly suitable for:

handling highly viscous fluids, as shear is low and the pump chambershave constant shape and volume (unless designed otherwise);

handling large pressure differentials with modest specific flow, asnumerous stages can readily be provided;

use as vacuum pumps and compressors, because they are fully scavenging;

handling fluids with significant gas or solids content (because of theirlow shear operation, and particularly if additional features are used toenhance solids handling or tolerance);

pumping applications that require a long, narrow form (e.g. ESP).

applications where positive displacement pumping with steady flow is ahigh priority (e.g. very dense materials, such as concrete; flowmetering or dosing, e.g. filling injection molds).

There are some important differences between conventional progressivecavity pumps (PCPs), and rotary machines having architectures asdescribed herein. In rotary machines having architectures as describedherein, there is a continuous line of contact between the rotor andstator. In some embodiments a metal spring seal (similar to a slinky toyor piston ring) can be used between the stator and rotor to provide apositive seal with no elastomer. In PCPs the stator is often made fromor lined with an elastomer, to provide sealing. This material oftendegrades and needs to be replaced. In PCPs, the rotor interacts with aparticular portion of the stator in at least two orientations. In rotarymachines as described herein, the moving line of contact along the ridgeof the helical rotor only interacts with the stator in one orientation,which can provide operational advantages. A transverse cross-section ofa typical PCP rotor-stator assembly shows a circular rotor positioned orcontained between two parallel sides of the stator profile. Thisarrangement limits the ability of the rotor to move when a foreignparticle such as sand or another hard substance becomes trapped in thiscontact region. The result is a potentially high abrasion condition. Therotor in rotary machines having architectures as described herein is notconstrained in this manner. Furthermore, the rotary machines describedherein have different flow characteristics than PCPs, which may be morefavorable for certain applications.

All-metal PCPs typically have lower volumetric efficiencies and loweroverall pump efficiencies than PCPs with an elastomer. The use of anelastomer in a PCP also typically enhances the solids handlingcapability of the pump versus an all-metal PCP, resulting in longeroperational lifetimes in many applications. For example, in one study ina high temperature oil well application, the overall efficiency of anall-metal pump ranged from about 20-50% with a lifetime of less than 500days, whereas a comparable elastomer PCP operated with efficiency in therange of 25-65% with about a 30 day longer lifetime. The efficiency ofboth types of PCP tends to decline quite rapidly during operation of thepump.

Embodiments of the helical trochoidal rotary machines described hereinhave been shown to provide high volumetric and overall efficiencies, andto operate with low degradation in efficiency over time.

EXAMPLE

Longevity testing was performed on a 2-stage helical trochoidal rotarypump (12 inches (30.48 cm) long, 2.8 inches (7.11 cm) diameter). Therotor and stator were made of 4140 hardened steel. The operating fluidwas mineral seal oil, a wellbore simulated fluid with a viscosity of 3cP, intended to simulate a downhole lift application of oil with watercut. The pump was operated at 400 RPM with the pressure set at 25 psiper stage (50 psi total), and the flow rate was 25 GPM. The pump wasoperated and tested under these conditions over a period of 136 days,which at 400 RPM represents 78 million cycles. FIG. 12 is a graphshowing the overall efficiency (plot A) and the volumetric efficiency(plot B) of the pump versus the number of cycles. Total efficiency is ameasure of how much shaft power is converted into useful work.Volumetric efficiency is a measure of slip. Slip is the ratio of actualflow delivered by a pump at a given pressure to its theoretical flow,where the theoretical flow can be calculated by multiplying the pump'sdisplacement per revolution by its driven speed. The observed volumetricand overall efficiency values are high, especially considering that boththe rotor and stator are made of metal, and the pump did not havedynamic seals on the rotor or stator. As can be seen from FIG. 12, thepump demonstrated very little loss in overall and volumetric efficiencyover the test period, and almost no loss over the first 70 millioncycles.

While particular elements, embodiments and applications of the presentinvention have been shown and described, it will be understood, that theinvention is not limited thereto since modifications can be made bythose skilled in the art without departing from the scope of the presentdisclosure, particularly in light of the foregoing teachings.

What is claimed is:
 1. A rotary machine comprising: a stator having astator length and a stator axis, and a rotor having a rotor length and arotor axis, said rotor disposed within said stator, said rotor, along atleast a portion of said rotor length, having a rotor helical profile,and a hypotrochoidal shape at any cross-section transverse to said rotoraxis, said stator, along at least a portion of said stator length,having a stator helical profile, and a stator shape at any cross-sectiontransverse to said stator axis that is an outer envelope formed whensaid hypotrochoidal shape of said rotor undergoes planetary motion,wherein said rotor is configured to undergo planetary motion within saidstator.
 2. The rotary machine of claim 1 wherein: said hypotrochoidalshape of said rotor has n lobes, where n is an integer; the stator shapehas (n−1) lobes; said rotor has a rotor pitch and a rotor lead; saidstator has a stator pitch and a stator lead; said rotor pitch is thesame as said stator pitch; and a ratio of said rotor lead to said statorlead is n:(n−1).
 3. The rotary machine of claim 2 wherein saidhypotrochoidal shape is an ellipse and n=2.
 4. The rotary machine ofclaim 3 wherein the rotary machine is a multi-stage machine and aplurality of chambers are formed between cooperating surfaces of saidrotor and said stator.
 5. The rotary machine of claim 4 wherein each ofsaid plurality of chambers has approximately the same dimensions andshape.
 6. The rotary machine of claim 4 wherein at least one of saidplurality of chambers has dimensions that are different from another ofsaid plurality of chambers.
 7. The rotary machine of claim 6 whereineach of said plurality of chambers has a different volume.
 8. The rotarymachine of claim 7 wherein said rotor pitch varies along at least aportion of said rotor length, and said stator pitch varies along atleast a portion of said stator length.
 9. The rotary machine of claim 7wherein said hypotrochoidal shape is an ellipse and the aspect ratio ofsaid ellipse varies along at least a portion of said rotor length. 10.The rotary machine of claim 7 wherein said rotor axis is inclinedrelative to said stator axis.
 11. The rotary machine of claim 1 whereinsaid rotary machine is a pump.
 12. The rotary machine of claim 7 whereinsaid rotary machine is a compressor or an expander.
 13. A rotary machinecomprising: a stator having a stator length and a stator axis, and arotor having a rotor length and a rotor axis, said rotor disposed withinsaid stator, said stator, along at least a portion of said statorlength, having a stator helical profile, and an epitrochoidal statorshape at any cross-section transverse to said stator axis, said rotor,along at least a portion of said rotor length, having a rotor helicalprofile, and a rotor shape at any cross-section transverse to said rotoraxis that is an inner envelope formed when said epitrochoidal statorshape undergoes planetary motion, wherein said rotor is configured toundergo planetary motion within said stator.
 14. The rotary machine ofclaim 13 wherein: the epitrochoidal stator shape has n−1 lobes, where nis an integer; said rotor shape has n lobes; said rotor has a rotorpitch and a rotor lead; said stator has a stator pitch and a statorlead; said rotor pitch is the same as said stator pitch; and a ratio ofsaid rotor lead to said stator lead is n:(n−1).
 15. The rotary machineof claim 14 wherein n=2.
 16. The rotary machine of claim 15 wherein therotary machine is a multi-stage machine and a plurality of chambers areformed between cooperating surfaces of said rotor and said stator, andeach of said plurality of chambers has approximately the same dimensionsand shape.
 17. The rotary machine of claim 15 wherein the rotary machineis a multi-stage machine and a plurality of chambers are formed betweencooperating surfaces of said rotor and said stator, and at least one ofsaid plurality of chambers has dimensions that are different fromanother of said plurality of chambers.
 18. The rotary machine of claim17 wherein each of said plurality of chambers has a different volume.19. The rotary machine of claim 18 wherein said rotor pitch varies alongat least a portion of said rotor length, and wherein said stator pitchvaries along at least a portion of said stator length.
 20. The rotarymachine of claim 18 wherein said rotor axis is inclined relative to saidstator axis.